1. Field of the Invention
The present invention relates generally to an apparatus and method for detecting noise in circuits. More specifically, the present invention provides a method and apparatus for detecting noise events in a system with time variable operating points.
2. Description of the Related Art
Power supply and power distribution system noise, especially dips due to large step activity increases in a microprocessor, are a limiting factor in how fast the circuits in such a processor can operate. This limits either the system operating frequency or limits chips that can yield at any given objective frequency. Traditionally, decoupling capacitors have been used to limit the magnitude of this noise. However, as design frequencies have risen over the years, decoupling capacitance is becoming either less effective at the frequencies that are required to have an effect, or are too costly in financial terms or power dissipation terms. That is, in terms of chip real estate and oxide leakage impact on chip power requirements.
Electrical distance from capacitor placement sites to circuits on chips constrained by physical space availability can make discrete capacitors completely or nearly ineffective. Therefore, it would be useful to have a mechanism for detecting noise events that indicate that further executions will cause the voltage in a circuit to dip to unacceptably low levels.
Current solutions may utilize a circuit with a precision direct current (DC) reference to determine if the noise being detected is of a sufficient magnitude to cause action to be taken. However, use of a fixed DC reference will not allow distinguishing between high frequency noise and other drift, set-point granularity, voltage drops due to current and power distribution resistance, and other low frequency and DC variances from the perfect reference. Drift is a low frequency fluctuation. Set-point granularity means that there are only finite discrete points that can be generated. Points between these finite points are off limits and cannot be generated. Therefore, it would be desirable to determine a way to address these issues in a cost effective manner by using the voltage being monitored as the reference.